Problem: With pumpkins having large variations in size and shape, it is not easy to design something that will work on a particular fruit. In order to ensure the design will transfer correctly to the individual pumpkin, it would be useful to know where the skin of the pumpkin would be whilst working in the 3D design application.
Solution: Use 123D Catch to create a 3D mesh of the lucky pumpkin, open the mesh in the 3D design software, and use it to ensure the desired cuts will work as intended.
The technique I used works well with pumpkins, but it could also be used for machining into other organic or random shapes.
Step 1: Place reference marks on pumpkin and take photos
In terms of taking pictures for use in 123D Catch, I would like to give a little bit of advice. First of all, don't bother spending lots of time building contraptions to automate the picture taking process. I know there are some plans published all over the internet, but I think your time is more wisely spent by studying and understanding the excellent tutorials on the 123D website: http://www.123dapp.com/catch/learn
Catch is very capable and as long as you follow the advice in the tutorials, very good results can be achieved by just using a hand held camera on it's own. One thing I noticed is that a lot of peoples, also some of the guys (m/f) with the automatic-picture-taking devices, only take a series of picture in a circle at a single elevation. The best results, as advised in the tutorials, is achieved by taking pictures at two elevations.